1. Field of the Invention
This invention relates to a magnetic recording/reproducing apparatus, such as a videotape recorder (VTR), which employs a lower-frequency-converted chrominance signal recording system.
2. Description of the Prior Art
Videotape recorders have become remarkably popular in recent years. Most of them employ the low-frequency-converted chrominance signal recording system (M system). The M-system is advantageous in that (1) the chrominance signal is hardly affected by fluctuations in the reproducing time base and (2) the chrominance signal can be recorded and reproduced with good linearity due to the high frequency biasing by the FM signal.
Block diagrams of signal recording and reproducing systems used for conventional VTRs are shown in FIGS. 1 and 2 respectively. For recording, a luminance signal is sent through the lowpass filter (LPF) 1, the frequency modulator 2 where the frequency of the signal is modulated, and the high pass filter (HPF) 3 to the mixer 4. Meanwhile, the chrominance signal is sent through the bandpass filter (BPF) 5, the auto color control circuit (ACC circuit) and the auto phase control circuit (APC circuit) 6, the balanced modulator 7 where the signal is modulated, and the lowpass filter (LPF) 8 to the mixer 4 where the signal is mixed with the luminance signal. The mixed signal is then sent to the recording head 10 through the recording amplifier 9.
For reproduction, the signal is transmitted through substantially the reverse sequence, as shown in FIG. 2, and outputted at the output terminal 21 as a reproduced video signal. Reference numeral 22 indicates the recording luminance signal system block, 23 the recording chrominance signal system block, 24 the reproduced luminance signal system block and 25 the reproduced chrominance signal system block. Signal operations which are well known have been briefly described above, though actual circuitry is more complex.
With the above construction, however, the color burst that has been converted to a low frequency (for example, 629 kHz) is recorded or reproduced for only about one-and-a-half wavelengths. In other words, if the output changes due to dropout or poor tape contact during the one-and-a-half wavelength reproducing time of the color burst, the APC and ACC circuits do not operate satisfactorily, causing color irregularity. This results in lateral noise on the monitor screen, the most conspicuous color noise.